Expandable and adjustable lordosis interbody fusion system

ABSTRACT

An expandable housing for an interbody fusion system has movable tapered external helical threaded members that travel along tracking to operably engage against the top and bottom shell members, urging them apart to cause expansion in the height of the housing. In an embodiment, the tapered members are disposed in a dual arrangement such that independent engagement of the tapered members along lateral portions of the top and bottom shells cause an angular tilt to the exterior surface of the housing when the tapered members are moved to different degrees. This function permits adjustment in the angular relationship between adjacent vertebrae and assists the lordotic adjustment of the patient&#39;s spine. When the functions of the device are used in combination by the surgeon, the device provides an effective tool for in situ adjustment when performing lateral lumbar interbody fusion.

RELATED APPLICATIONS

The present U.S. non-provisional patent application is related to andclaims priority benefit to an earlier-filed provisional patentapplication titled EXPANDABLE LATERAL INTERBODY FUSION SYSTEM, Ser. No.61/871,780, filed Aug. 29, 2013. The identified earlier-filedapplication is hereby incorporated by reference into the presentapplication as though fully set forth herein.

FIELD OF THE INVENTION

The invention relates to surgical procedures and apparatus for treatinglumbar back pain.

BACKGROUND OF THE INVENTION

Lumbar spinal fusion is a surgical procedure to correct problemsrelating to the human spine. It generally involves removing damaged discand bone from between two vertebrae and inserting bone graft materialthat promotes bone growth. As the bone grows, the two vertebrae join, orfuse, together. Fusing the bones together can help make that particulararea of the back more stable and help reduce problems related to nerveirritation at the site of the fusion. Fusions can be done at one or moresegments of the spine.

Interbody fusion is a common procedure to remove the nucleus pulposusand or the annulus fibrosus that compose the intervertebral disc at thepoint of the back problem and replace it with a cage configured in shapeand dimension to restore the distance between adjacent vertebrae to thatof a proper condition. Surgical approaches to implement interbody fusionvary, and access to the patient's vertebral column can be made throughthe abdomen or back. One other surgical method for accomplishing lumbarspinal fusion in a less invasive way involves accessing the vertebralcolumn through a small incision on the side of the body. This procedureis known as lateral lumbar interbody fusion.

Once the intervertebral disc is removed from the body during the laterallumbar interbody fusion, the surgeon typically forces different trialimplants between the vertebral endplates of the specific region todetermine the appropriate size of the implant for maintaining a distancebetween the adjacent vertebrae. Another consideration is to maintain thenatural angle between lumbar vertebral bodies to accommodate thelordosis, or natural curvature, of the spine. Therefore, duringselection of a cage for implantation, both intervertebral disc heightand lordosis must be considered. Prior art fusion cages are oftenpre-configured to have top and bottom surfaces angles to one another toaccommodate the natural curvature of the spine. It is unlikely thatthese values can be determined precisely prior to the operation, whichis a drawback in present procedures. Prepared bone graft is generallypacked into the cage implant once it is properly sized and before it isinserted in between the vertebral bodies.

Present lateral interbody fusion cage devices are generally limited toproviding height expansion functions, but not a lordotic adjustmentcapability. In implementing a trial-and-error approach to sizing andfitting the interbody fusion cage into the target region for theparticular geometric configuration for that patient, the patient issubjected to significant invasive activity. The bone graft material isgenerally added and packed in to the fusion device after the desiredheight expansion has been reached and final adjustments made.

SUMMARY OF THE INVENTION

An embodiment of the device comprises an expandable housing comprised ofopposing shell members. Movable tapered screw-like elements having anexternal helical thread are disposed in the housing and operably engageagainst the top and bottom shell members, urging them apart to causeexpansion in the height of the housing. This function permits adjustmentof the distance (height) between adjacent vertebrae when in place. Thetapered members are disposed in a dual arrangement such that independentengagement of the tapered members along lateral portions of the top andbottom shells cause an angular tilt to the exterior surface of thehousing when the wedge members are moved to different degrees. Thisfunction permits adjustment in the angular relationship between adjacentvertebrae and assists the lordotic adjustment of the patient's spine.When the functions of the device are used in combination by the surgeon,the device provides an effective tool for in situ adjustment whenperforming lateral lumbar interbody fusion.

An embodiment of the device further comprises a track configurationwithin the housing for guiding the tapered external helical threadedmembers in their engagement with the top and bottom shell members. Thetrack comprises raised elements on each of the interior surfaces of thetop and bottom shell members that permit an interlocking engagement forlateral stability of the housing when in a contracted position. As thehousing expands, the track area provides space for storage of bone graftmaterial. One embodiment may provide for an elastic membrane to bepositioned around the housing to prevent bone graft material fromseeping out of the cage and to provide a compressive force around thecage to provide structural stability to the housing.

An embodiment of the device further comprises drive shafts for operatingthe tapered external helical threaded members. The drive shafts permitthe surgeon, through the use of a supplemental tool, to manipulate theshafts which operatively move the tapered external helical threadedmembers in controlling the expansion of the housing and angularadjustment of the top and bottom shell members for in situ fitting ofthe interbody fusion device. A locking mechanism is provided forpreventing rotation of the shafts when the tool is not engaged and aftermanipulation by the tool is completed. The tool also facilitatesinsertion of bone graft material into the fusion body during in situadjustment.

An embodiment of the present invention provides a surgeon with theability to both expand the fusion cage and adjust the lordotic angle ofthe fusion cage in situ during operation on a patient and to introducebone graft material at the operation site while the device is in place.This embodiment of the present invention therefore provides a fusioncage having geometric variability to accommodate the spinal conditionunique to each patient.

Embodiments of the present invention therefore provide an interbody cagedevice for use in lateral lumbar interbody fusion procedures thatcombines the functions of height expansion for adjusting the distancebetween adjacent vertebrae with lordotic adjustment to control theangular relationship between the vertebrae. Embodiments of the inventiveinterbody cage device further provide a storage capacity for containingbone graft material in the interbody cage device as disc height andlordotic adjustment takes place in situ.

The present invention also provides a device that may be used inenvironments other than in interbody fusion applications. It maygenerally be used to impart a separating effect between adjacentelements and to impart a variable angular relationship between theelements to which it is applied.

These and other features of the present invention are described ingreater detail below in the section titled DETAILED DESCRIPTION OF THEINVENTION.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

An embodiment of the present invention is described herein withreference to the following drawing figures, with greater emphasis beingplaced on clarity rather than scale:

FIG. 1 is a view in side elevation from the side of the expandable shelldevice.

FIG. 2 is a perspective view of a bottom section of the expandableshell.

FIG. 3 is a top plan view of the bottom section of the expandable shell.

FIG. 4 is a top plan view of the expandable shell device.

FIG. 5 is a perspective view of a tapered external helical threadedmember.

FIG. 5A is a view in side elevation from the side of the taperedexternal helical threaded member.

FIG. 5B is a view in side elevation from the front of the taperedexternal helical threaded member.

FIG. 6 is a cross-sectional view of the device taken along lines 6-6 inFIG. 1.

FIGS. 7A-7C are a series of views in side elevation of the device as itundergoes expansion.

FIG. 8 is a view in side elevation of the device showing an expansion ofthe device to accommodate a lordotic effect.

FIG. 9A is a perspective expanded view of thrust bearing for the driveshaft.

FIG. 9B is a perspective view of the drive shafts and thrust bearings.

FIG. 9C is a top plan view in cross section of the area of engagement ofthe drive shafts with the thrust bearings.

FIG. 10 is a side elevation view of the housing as expanded.

FIG. 11A is a top plan view of another embodiment of the device.

FIG. 11B is a top plan view of yet another embodiment of the device.

FIG. 12A is a top plan view of the drive shafts disengaged by thelocking mechanism.

FIG. 12B is a top plan view of the drive shafts engaged by the lockingmechanism.

FIG. 13A is a perspective view of the locking mechanism.

FIG. 13B is a top plan cross sectional view of the drive shaftsdisengaged by the locking mechanism.

FIG. 13C is a top plan cross sectional view of the drive shafts engagedby the locking mechanism.

FIG. 14 is a view taken along lines 14-14 in FIG. 11A.

FIGS. 15A-C are a series of views in side elevation taken from the endof the device as it undergoes expansion showing the lordotic effect.

FIG. 16 is a perspective view of the operating tool.

FIG. 17 is a view showing a manner of attachment of the operating toolto the drive shafts of the device.

FIG. 18 is a breakaway perspective view of the handle of the operatingtool.

FIG. 19 is a perspective view of gears in the handle engaged foroperation of both drive shafts.

FIG. 20 is a perspective view of gears in the handle disengaged foroperation of a single drive shaft.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the drawings figures, an interbody fusion body deviceis herein described, shown, and otherwise disclosed in accordance withvarious embodiments, including preferred embodiments, of the presentinvention. The interbody fusion device 10 is shown generally in FIG. 1.It is comprised of a housing 12 having a top shell 14 and a bottom shell16. The overall housing may have a length of 50 mm and a width of 20 mm,as an example. The shell material may be comprised of a suitablematerials, such as titanium alloy (Ti-6AL-4V), cobalt chromium, orpolyether ether ketone (PEEK). Other materials may be suitable that canprovide sufficient compositional integrity and that have suitablebiocompatible qualities. The interior of the shells are configured witha cascading step tracking 18 and 20 placed along their lateral edges. Asshown in FIG. 2, step tracking 18 begins towards the midpoint of aninner surface of bottom shell 16 with successive track steps increasingin height as the tracking extends to a first end of bottom shell 16.Correspondingly, step-tracking 20 begins towards the midpoint of theinner surface of bottom shell 16 with successive track steps increasingin height as that portion of the tracking extends to a second oppositeend of bottom shell 16. Step tracking 18 comprises dual track runs 22and 24 while step tracking 20 comprises dual track runs 26 and 28 asshown in FIG. 3. Corresponding step tracking 30 and 32 is provided ontop shell 14 as shown in FIG. 4. When the device is in its fullycompressed state where top shell 14 lies adjacent to bottom shell 16, asshown in FIG. 1, step tracking 18 intermeshes with step tracking 30 andstep tracking 20 intermeshes with step tracking 32.

The respective track runs comprise a series of risers, or track steps,which are spaced apart to receive the threads of tapered externalhelical threaded members. The tapered external helical threaded membersprovide a wedging action for separating the top and bottom shell therebyincreasing the height of the housing to effect expansion between thevertebral bodies in which the device is placed. As shown in FIG. 4,track run 22 receives tapered external helical threaded member 34, trackrun 24 receives tapered external helical threaded member 36, track run26 receives tapered external helical threaded member 38, and track run28 receives tapered external helical threaded member 40. Track run 22aligns collinearly with track run 26 such that the travel of taperedexternal helical threaded members 34 and 38 within the respective trackruns occurs within that collinear alignment. The thread orientation oftapered external helical threaded members 34 and 38 are opposite of eachother such that their rotation will result in opposite directionalmovement with respect to each other. As shown in FIG. 4, a drive shaft42 runs along the collinear span of track runs 22 and 26 and passesthrough tapered external helical threaded members 34 and 38. Shaft 42has a square cross sectional configuration for engaging and turning thetapered external helical threaded members. As shown in FIG. 5, thecentral axial opening 44 of the tapered external helical threadedmembers are configured to receive and engage the shaft 42. Shaft 42 mayalternatively comprise any shape for effectively creating a spline, suchas a hexagonal shape, and central axial openings 44 may comprise acorresponding configuration for receiving that shape. As shaft 42 isrotated by its end 48 in a clockwise direction, tapered external helicalthreaded members 34 and 38 are rotated and their respective threadorientations cause the screws to travel apart from each other alongtrack run 22 and track run 26, respectively. Correspondingly, as shaft42 is rotated by its end 48 in a counter-clockwise direction, taperedexternal helical threaded members 34 and 38 are caused to travel towardseach other along track run 22 and track run 26, respectively.

Similarly, track run 24 aligns collinearly with track run 28 such thatthe travel of tapered external helical threaded members 36 and 40 withinthe respective track runs occurs within that collinear alignment. Thethread orientation of tapered external helical threaded members 36 and40 are opposite of each other such that their rotation will result inopposite directional movement with respect to each other. Also, shaft 46passes through and engages tapered external helical threaded members 36and 40. However, the orientation of tapered external helical threadedmembers 36 and 40 is reversed from the orientation of tapered externalhelical threaded members 34 and 38. Under this orientation, as shaft 46is rotated by its end 50 in a counter-clockwise direction, taperedexternal helical threaded members 36 and 40 are rotated and theirrespective thread orientations cause the screws to travel apart fromeach other along track run 24 and track run 28, respectively.Correspondingly, as shaft 46 is rotated by its end 50 in a clockwisedirection, tapered external helical threaded members 36 and 40 arecaused to travel towards each other along track run 24 and track run 28,respectively.

As shown in FIG. 2, the step tracking is configured with a cascadingseries of risers of increasing height. For example, each track run hasrisers 52-60 as shown for step tracking 18 in FIG. 2. As the thread of atapered external helical threaded member travels into the gap betweenriser 52 and 54, the positional height of the tapered external helicalthreaded member body, as supported on risers 52 and 54, increases withinthe housing 12. As the tapered external helical threaded membercontinues to travel along the track run, its thread passes from the gapbetween risers 52 and 54 and enters the gap between risers 54 and 56which raises the tapered external helical threaded member body furtherwithin housing 12 as it is supported on risers 54 and 56. As the taperedexternal helical threaded member continues its travel along theremainder of the step risers 58 and 60 its positional height increasesfurther. As the positional height of the tapered external helicalthreaded member body increases, it urges top shell 14 apart from bottomshell 16 as shown in the series of FIGS. 7A-7C. The combined effect ofrotating the tapered external helical threaded members to cause theirmovement towards the outer ends of the respective track runs causes anexpansion of the housing 12 as shown in FIG. 7. The fully expanded shellis shown in FIG. 10. The housing 12 may be contracted by reversing themovement of the tapered external helical threaded members such that theytravel back along their respective track runs towards the midpoint ofthe housing. The housing will optimally provide expansion andcontraction to give the implant device a height over a range of aroundapproximately 7.8 mm to 16.15 mm in the present embodiment. The deviceof this embodiment of the invention can be adapted to provide differentexpansion dimensions.

The pairs of tapered external helical threaded members in each collineardual track run may be rotated independently of the pair of taperedexternal helical threaded members in the parallel track run. In thisarrangement, the degree of expansion of that portion of the housing overeach collinear track run may be varied to adjust the lordotic effect ofthe device. As an example shown in FIG. 8, tapered external helicalthreaded members 36 and 40 have been extended to a particular distancealong track run 24 and track run 28, respectively, causing the top shell14 to separate from bottom shell 16 thereby expanding housing 12.Tapered external helical threaded members 34 and 38 have been extendedto a lesser distance along parallel track run 22 and 26, respectively,causing that portion of the top shell over track runs 22 and 26 toseparate from bottom shell to a lesser degree. The series of FIGS.15A-15C show this effect where tapered external helical threaded members36 and 40 are extended apart from each other in further increasingincrements where the tapered external helical threaded members 34 and 38maintain the same relative distance to each other.

In FIG. 15A, the respective positioning of the set of tapered externalhelical threaded members 36-40 is approximately the same as the set oftapered external helical threaded members 34-38 in their respectivetracking. In this position, the top shell 14 is essentially parallelwith bottom shell 16. In FIG. 15B, the set of tapered external helicalthreaded members 36-40 move further distally apart along their trackingas the set of tapered external helical threaded members 34-38 remains attheir same position in FIG. 15A. In this setting, the lateral edge oftop shell 14 along which tapered external helical threaded members 36and 40 travel is moved higher with respect to the lateral edge of topshell 14 along which tapered external helical threaded members 34 and 38travel, giving a tilt to top shell 14 with respect to bottom shell 16.In FIG. 15C, the set of tapered external helical threaded members 36-40move even further distally apart along their tracking with respect tothat of the set of tapered external helical threaded members 34-38,giving an even greater tilt to top shell 14 with respect to bottom shell16. Through the independent movement of the respective tapered externalhelical threaded member sets, the device can achieve a lordotic effectof between 0° and 35° in the present embodiment. The device of thisembodiment of the invention can be adapted to provide different lordotictilt dimensions.

The tapered external helical threaded members have a configurationcomprising a body profile that has an increasing minor diameter fromD_(r1) to D_(r2) as shown in FIG. 5. The threads 33 have a pitch tomatch the spacing between the riser elements 52-60 in the tracking runsas shown in FIG. 4. Threads 33 can have a square profile to match theconfiguration between the risers, but other thread shapes can be used asappropriate. The increasing diameter and tapering aspect of the helicalthreaded members cause top shell 14 and bottom shell 16 to move apart asdescribed above. The contact at the tops of the risers 52-60 is made atthe minor diameter of the helical threaded member.

Thrust bearings are provided to limit the axial direction motion of thedrive shafts within shell 12. As shown in FIG. 9A, thrust bearing 62comprises a two-piece yoke configuration that mate together andpress-fit around ends of the shafts. The top part 64 of the thrustbearing yoke defines openings for receiving a round portion 66 of theshaft ends. In FIG. 9C, square shaft 42 has a rounded portion 66 oflesser diameter than the square portion of the shaft. A mating piece 65of the thrust bearing engages with top part 64 to encircle the roundedportion 66 of drive shaft 42. Pin elements 68 in the top portion 64 andbottom portion 65 engages a corresponding holes 69 in the mating pieceto provide a press fit of the thrust bearing around the shaft. Journalgrooves 67 can also be provided in thrust bearing 62. Shaft 42 can havean annular ridge 63 around its rounded portion 66 which is received injournal groove 67 as shown in FIG. 9C. A thrust bearing is provided ateach end of the drive shafts as shown in FIG. 9B. As shown in FIG. 6,the thrust bearings restrict the axial movement of the drive shafts inthe housing.

A safety lock is provided at the proximal end of the device forpreventing unintended rotation of the shafts. As shown in FIGS. 12A and12B, safety lock member 70 is provided for engagement with the proximalends of drive shafts 42 and 46. The openings 73 in safety lock member 70are configured with the shape of the cross-sectional configuration ofthe drive shafts (see FIG. 13A). A portion of the drive shafts has anarrowed, rounded configuration 71 such that the drive shaft can rotatefreely while the rounded portion of the shaft is in alignment with thesafety lock member openings 73 (see FIG. 13C). FIG. 12B shows thisrelationship among the safety lock member 70, thrust bearing 62 anddrive shafts 42 and 46. When the non-narrowed portions 75 of the shaftsare placed in alignment with the safety lock member openings 73, thenrotation of the shafts is prevented (see FIG. 13B). FIG. 12A shows thisrelationship among the safety lock member 70, thrust bearing 62 anddrive shafts 42 and 46. A compression spring 77 can be placed betweenthrust bearing 62 and safety lock member 70 to urge safety lock memberback over the square portion 75 of the drive shafts. FIG. 12B shows alock disengagement when the safety lock member 70 is pushed forward outof alignment with the square portions 75 and placed in alignment withthe rounded portions 71 of shafts 42 and 46. Post 79 can be disposedbetween safety lock member 70 and thrust bearing 62 on which compressionspring 77 can be positioned. Post 79 can be fixedly connected to safetylock member 70 and an opening can be provided in thrust bearing 62through which post 79 can slide. Post 79 is provided with head 81 tolimit the backward movement of safety lock member 70 from thecompressive force of spring 77.

The interaction of the tapered external helical threaded members withthe step tracking contributes to self-locking under a power screwtheory. In considering the variables for promoting a self-locking aspectof the tapered threaded members, certain factors are relevant. Inparticular, those factors include the coefficient of friction of thematerials used, such as Ti-6Al-4V grade 5, the length of pitch of thehelical threads and the mean diameter of the tapered member. Thefollowing equation explains the relationship among these factors indetermining whether the tapered external helical threaded members canself-lock as it travels along the step tracking:

$T_{R} = {\frac{{Fd}_{m}}{2}\left( \frac{l + {\pi\;{fd}_{m}{seca}}}{{\pi\; d_{m}} - {{fl}\mspace{14mu}{seca}}} \right)}$

The above equation determines the torque necessary to apply to the driveshafts engaging the tapered external helical threaded members forexpanding the shell members. This torque is dependent upon the meandiameter of the tapered external helical threaded members, the load (F)applied by the adjacent vertebral bodies, the coefficient of friction(f) of the working material, and the lead (l) or, in this embodiment,the pitch of the helical threading. All of these factors determine therequired operating torque to transform rotational motion into a linearlift to separate the shell members in accomplishing expansion andlordosis.

The following equation describes the relationship among the factorsrelating to the torque required to reverse the tapered external helicalthreaded members back down the tracking:

$T_{R} = {\frac{{Fd}_{m}}{2}\left( \frac{{\pi\;{fd}_{m}} - l}{{\pi\; d_{m}} + {fl}} \right)}$

Under this equation, the torque required to lower the tapered externalhelical threaded members (T_(L)) must be a positive value. When thevalue of (T_(L)) is zero or positive, self-locking of the taperedexternal helical threaded members within the step tracking is achieved.If the value of (T_(L)) falls to a negative value, the tapered externalhelical threaded members are no longer self-locking within the steptracking. The factors that can contribute to a failure to self-lockinclude the compressive load from the vertebral bodies, the pitch andmean diameter of the helical thread not being adequately great, and aninsufficient coefficient of friction of the material. The condition forself-locking is shown below:πfd _(m) >l

Under this condition, it is necessary to select an appropriatecombination of sufficient mean diameter size of the tapered member,along with the product material being a greater multiple than the leador pitch in this particular application so that the tapered members canbe self-locking within the step tracking. Based upon average values witha patient lying on their side, the lumbar vertebral body cross sectionalarea is around 2239 mm² and the axial compressive force at that area is86.35 N. With the working material selected to be Ti-6Al-4V, theoperating torque to expand shell housing 12 between L4-L5 of thevertebral column is around 1.312 lb-in (0.148 N-m), and the operatingtorque to contract shell housing 12 between L4-L5 of the vertebralcolumn is around 0.264 lb-in (0.029 N-m).

Alternate embodiments of the expandable shell housing provide fordifferent surgical approaches. FIG. 11A shows housing 100 for use wherea surgeon approaches the lumbar area from an anterior aspect of thepatient. The general configuration of the tracking runs for thisembodiment is similar to that for device 10, but the drive shafts formoving the tapered external helical threaded members are applied with atorque delivered from a perpendicular approach. For this, a dual set ofworm gears 102 and 104 respectively transfer torque to drive shafts 106and 108 as shown in FIG. 14.

FIG. 11B shows housing 200 for use where a surgeon approaches the lumbararea from a transforaminal aspect of the patient. The generalconfiguration of the tracking runs for this embodiment is also similarto that for device 10, but the torque is applied to the drive shaftsfrom an offset approach. For this, a dual set of bevel gears (not shown)may be used to transfer torque to drive shafts 206 and 208.

Housing 12 is provided with numerous niches and open areas in itssurface and interior regions to accommodate the storage of bone graftingmaterial. The interstitial spaces between the risers of the cascadingstep tracking also offers areas for receiving bone-grafting material. Amembrane can be provided as a supplement around housing 12 to helpmaintain compression on the top and bottom shells and to hold in bonegrafting material. Tension spring elements 78 can be provided to holdtogether top member 14 and bottom member 16 as shown in FIG. 10. Theseelements may also serve to provide an initial tension force in thedirection opposite of the expansion against the interbody fusion device.This allows the tapered external helical threaded members to climb therisers in the event that contact between the outer shells and thevertebral bodies is not yet made.

Accordingly, this embodiment of the interbody fusion device of theinstant invention is capable of expansion to provide support betweenvertebral bodies and accommodate the load placed on that region.Furthermore, the inventive interbody fusion device is capable ofachieving a configuration that can provide an appropriate lordotic tiltto the affected region. The device, therefore, provides a significantimprovement with regards to patient-specific disc height adjustment.

The device is provided with a tool for operating the interbody fusiondevice as it is adjusted in situ in a patient's spine. The operatingtool 300 is shown generally in FIG. 16 and comprises a handle member302, a gear housing 304 and torque rod members 306 and 308. The torquerod members connect to the drive shafts of expandable shell 12. Oneembodiment for connecting the torque rod members to the drive shafts ofexpandable shell 12 is shown in FIG. 17. In this arrangement, ends 48and 50 of drive shafts 42 and 46 can be provided with a hex-shaped head.The ends of torque rod members 306 and 308 can be provided withcorrespondingly shaped receivers for clamping around ends 48 and 50.

Within the gear housing 304, handle member 302 directly drives torquerod member 308. Torque rod member 308 is provided with spur gear member310 and torque rod member 306 is provided with spur gear member 312.Spur gear 312 is slidably received on torque rod member 306 and can movein and out of engagement with spur gear 310. Spur gear lever 314 engageswith spur gear 312 for moving spur gear 312 into and out of engagementwith spur gear 310. When torque rod member 308 is rotated by handle 302,and spur gear 312 is engaged with spur gear 310, rotation is translatedto torque rod member 306. In this condition, torque rod member 308rotates drive shaft 46 simultaneously with torque rod member 306 rotatesdrive shaft 42 to effect expansion of shell 12 as shown in FIGS. 7A-7C.Spur gear 312 can be moved out of engagement with spur gear 310 byretracting spur gear lever 314 as shown in FIG. 20. With spur gear 312out of engagement with spur gear 310, rotation of handle 302 only turnstorque rod member 310. In this condition, torque rod member 308 rotatesdrive shaft 46 solely and drive shaft 42 remains inactive to effect thetilt to the top member of shell 12 as shown in FIG. 8 and FIGS. 15A-15Cto achieve lordosis.

To achieve expansion of the device in the described embodiment, theoperator will turn handle member 302 clockwise to engage torquing. Thisapplied torque will then engage the compound reverted spur gear traincomposed of spur gear members 310 and 312. This series of gears willthen spin torque rod members 306 and 308 in opposite directions of eachother. Torque rod member 310 (in alignment with handle member 302) willspin clockwise (to the right) and torque rod member 306 will spincounterclockwise (to the left). The torque rod members will then rotatethe drive shafts of interbody fusion device 12 expanding it to thedesired height.

To achieve lordosis the operator will move the spur gear lever 314 backtowards handle member 302. By doing so spur gear 312 connected to torquerod member 306 is disengaged from the overall gear train, which in turnwill disengage torque rod member 306. As a result, torque rod member 308will be the only one engaged with the interbody fusion device 12. Thiswill allow the operator to contract the posterior side of the implantdevice to create the desired degree of lordosis.

Although the invention has been disclosed with reference to variousparticular embodiments, it is understood that equivalents may beemployed and substitutions made herein without departing from the scopeof the invention.

Having thus described the preferred embodiment of the invention, what isclaimed as new and desired to be protected by Letters Patent includesthe following:

The invention claimed is:
 1. A spinal implant device for placementbetween vertebral bodies, the device comprising: an expandable shell; atleast one wedge member; at least one drive shaft; and the expandableshell comprising a top member and a bottom member separate from eachother, at least the bottom member having tracking for receiving the atleast one wedge member, the at least one drive shaft engaging with thetop member, the bottom member, and the at least one wedge member formoving the at least one wedge member along the tracking, the at leastone wedge member engaging the top member and the bottom member, the atleast one wedge member comprising a tapered configuration having anexternal helical thread, whereby the top member and bottom member moverelative to each other in response to rotation of the at least one wedgemember along the tracking to effect an expansion of the shell, thetracking comprising a cascading series of risers on interior surfaces ofeach of the top and bottom members, the cascading series of riserscomprising individual riser members increasing in height along theinterior surfaces and delivering corresponding staggered spaces inbetween the individual riser members so that the individual risermembers and corresponding spaces on the top member overlap theindividual riser members and corresponding spaces on the bottom member,permitting an interlocking engagement of the two members when the twomembers are in a contracted position, and wherein the tracking isconfigured to increase a longitudinal position of the at least one wedgemember along and relative to the interior surfaces of the top and bottommembers within the shell as it travels along the tracking whereby the atleast one wedge member engages the top and bottom members to selectivelycontact the shell.
 2. The spinal implant device of claim 1 in which thethread of the at least one wedge member is received in the staggeredspaces between the individual riser members for guiding the at least onewedge member along the tracking, the at least one wedge member beingcapable of engaging with a plurality of adjacent riser members ofdifferent heights simultaneously, a minor diameter of the at least onewedge member engaging top edges of the individual riser members.
 3. Thespinal implant device of claim 1, wherein the height of the cascadingseries of risers increases from a middle portion of the shell to anedge.
 4. The spinal implant device of claim 1, wherein the height of thecascading series of risers increases from a middle portion of the shellto a first edge and from the middle portion of the shell to a secondedge.